Purification of magnesium and magnesium alloys.



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BERTI-IOLD HOEFMANN AND ROBERT SUCHY. 0F GRIESHEIM-ON-TI-IE-MAIN, GERMANY,

ASSIGNORS TO CHEMISCHE FABRIK GRIESI-IEIM-ELEKTRON, OF FRANKFORT-ON- THE-MAIN, GERMANY, A CORPORATION OF GERMANY.

PURIFICATION OF MAGNESIUM AND MAGNESIUM ALLOYS.

No Drawing.

Specification of Letters Patent. Patented May 30, 1911, Application filed September 28, 1910. Serial No. 584,333.

To all whom itmay concern: 7

Be it known that we, BERTHOLD HOFFMANN and ROBERT Svonr, subjects of the German Emperor, and residents at Griesheim-on-the- -Main, Germany, have invented certain new of the .air causes eitlorescences of magnesia which take place according to Lemoine (see Uhcmiscizes Zemralblatt 1899 Vol. II page 516) in accordance wit-h theequation:

Chlorid-l-mMgO-i-mH as long as moisture is present and the metal is corroded at the places where such chlorid is present. The presence of said chlorid arises both. from the manufacture of the metal and from the usual methods of purification of magnesium and alloys of magnesium hitherto adopted. The metal has been subjected to a process for purification either by fusing it again with carnallite, as indicated by Borchers on page 18 of his EZe/ctro-Mctal- Zurg-y 1901, or by melting with alkali-chlorid as proposed by Detille and Caron (see Annales (Z0 Oilmic et de Physique, 3rd series, Vol. 67, page 340 (1863)). The molten metal has a specific gravity which is near that of the molten chlorid, so that there is no absolute separation of the chlorid and metal. Perfectly pure magnesium, freefrom chlorid, has already been obtained by dis tilling the metal (see for instance Abegg, Han/[buck (Z01 Anorg. Che-mic :lI, page 36, 1905, or Sonst/idt Jahrcsberz'clzte (1863) page 737) but it is obvious that such distillation on a large scale is not available owing to the impracticability of fulfilling the unusual requirements as regards the material for the vessels, due to the boiling point of the metal which is about 2200 Centigrade (see R. Schenks Pkg 827ml. Chemie der Metalle 1909, page 4) and owing to the readiness with which the metal combines with the elements of the air. Owing to the valuable properties of pure magnesium and pure magnesium alloys in the metal industry, a process which will remove all traces of chlorid in an economical and advantageous manner is very desirable.

Vi e have discovered that it is possible to readily and completely free magnesium and alloys thereof from all traces of chlorid by passing through the molten metal, hydrogen, or other gas which is inert as regards magnesium. Such gas will drive off every trace of the chlorid'at temperatures which are but little higher than the melting point of the chlorid.

The process may be carried out in the following manner but the invent-ion is not limited thereto. A crucible is charged with 8 kilograms of the metal, or alloy, to be purified which may be either magnesium, or a prepared magnesium alloy, or the components of a magnesium alloy. The crucible is then closed by a cover which carries a hydrogen supply pipe extending almost to the bottom of the crucible, and a notch, or a gas outlet pipe. Then a current of hydrogen is passed at a moderate velocity through the fluid metal for 5, or 6, hours at a temperature of from 800 to 900, centigrade. The hydrogen issuing from the crucible carries away with it the chlorid up to the very last traces thereof. The time required for the purifying operation varies, of course, within certain limits, depending on the temperature, the velocity of the gas through the metal, and the amount of metal treated.

The hydrogen or other inert gas can, if desired, be passed over the fluid metal which may be kept inzmot-ion by any suitable means. The gas may also be drawn over, or through, the bath at a reduced pressure and thus effeet a removal of the chlorid at a temperature lower than that employed when the operation is carried out under normal pressure, or higher pressures obtained by any suitable means may be employed. Furthermore We have found that the time within which the purifying process is carried out and the temperature at which it takes place can be reduced considerably if in lieu of dry hydrogen or other indifferent gas a wet gas be purified and on thedegree of wetness-of" the gas. In carrying out'the process care v products of the water.

is employed. In this casethe action of the dry gas by which the chlorids-contained in' the metal are vaporized, is assisted bythechemical action-of the water on the chlorids according-to the equations MgGl ri oz ugo 21101 .MgO+MgCl =Mg -O Cl and Therefore from the chlorid. are formed" hydrochloric acid, according to the first equation, which acid. is carried off by the hydrogen, and also oxychlorid of magnesium,

according to the secondequation, which floats on the metal and can easily be removed. 'In thisway one and the same mass of metal is'purifiedbywet gas within 1 to- 2' hours and at a temperature of only 700 to 800 centigrade, while with dry gas the process requires 5 to 6 hours and a temperature of 800 to. 900 C. Of course wet gas can also be employed at'highertemperatures .whcnthe time of purifyingis short-- ened. It is also aanattcr of course that the time within which the purification takes place dependson the velocity of the passagev of the ,gas,'-o11 the'quantity ofthe metalto has to be taken'thatno considerable drops of water come into the fluid .gasfbecause otherwise the reaction Mg-le'H Oz-MgO-f-H' would take place with great vehemencc and the consequence would be. a loss of metal.

In employing wet gas "the process may be carried out as follows: The purified dry hydrogen is led through water or steam or a spray of water is admitted to it and before its entrance into the cover of the crucible the thuswetted hydrogen is again sufliciently heated to vaporize again any condensation It is sufficient to conduct the wet hydrogen over the surface of the'liquid metal if by a stirrer or the like care is taken thatalways new chlorid con taining metal is forwarded to the surface. The hydrogen which leaves the crucible may be purified from the. substances itcarries with it, by any suitable means,-as for instance'by washing-it with water and then used again. By this continuous circulation the expenditure of the gas is very small.

We claim:

1. The herein described process of purifying magnesium and its alloys from chlorids which consists inbringing a current of an indifferent-gas into contact with the molten indifferent gas'into contact with-the molten metalat a temperature above the vaporizing point of the chlorid and stirring the metal duringthe passage of the current.

4. The herein described process of purifyin gmagnesium and its alloys from chlorids which consists. 1D. bringing a-current of hydrogen into contact with the molten metal at a temperature aboveathe vaporizing point of the chlorid and-stirring themetal during the passage ott-he current.

5. The herein described process of purityinginagnesium and itsalloys from chlorids which consists in bringing a current of a Wet indifferent gas into contact with the molten metal at a temperature above the vaporizing point I of the chlorid.

'6. The herein described p-rocess of purifying magnesium and its alloys from chlorids whichconsists'inpbringing a current of wet i hydrogen-into contact with the molten metal at a temperature aboveithe vaporizing point of the chlorid.

i7. .The hereindescribed process of purifying magnesiumand its alloys from chlorids which consists in bringing a current of a wet indifferent gas 'into contact with the molten metal v at a temperature above the vaporizing point of'the chlorid and stirring the metal during-the-passage of the current.

8. The herein described process of purifvin; magnesium and its alloys from chlorids whichconsists in bringing a current of wet hydrogeminto contact-with the molten metal .at a temperature above'the vaporizing point of the, chlori'dv and stirring the metal during the passage of the current.

In testimony whereof .we have-signed our names to this specification 'inthe presence of two subscribing witnesses.

'BERTHOLD HOFFMANN. ROBERT SUOHY.

Witnesses ffor-both. applicants FRANZ EHASSLABHER, EBWIN .DIPPEL. 

